Thin cemented carbide disk



A Feb. 12, 1935. F. TAYLQR.

THIN CEMENTED CABIDE DISK Original Filed Sept 8, 1930.

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Patented Feb. 12, 1935 THIN CEMENTED CARBID DISK Taylor, Niskayilna, N. Y., assignor to Electric Company, a,v corporation o1 Original application Se 17, 1932, Serial No.

division ofv my copending 80,330, filed September 8, aking strong,

'I'his application is a application Serial No. 4 1930, and entitled.

thin, cemented carbide disks.

'I'he present inventi ture of strong, thin, bide disks, andparti acter which have a and are suitable-fo Cemented c and are disclos #1,549,615 and #1,721, generally consist of a sinter bide for example tungste y cementing or binder medium which has a lower melting point than' the c cobalt, the cobalt usu about 3 to about V207 with the remainder tung tungsten carbide and cobalt provide the pre composition other carbide such as molybdenum r elements such as nickel, uranium may be employed Method of m on relates to the manufacne-grained, cemented car-v. cularlyto disks of this charcentral opening therethrough r use as glass cutters and the arbide compositions are well ed in Schrter Patents Such compositions ed mixture of a car-fx n carbide, with ai' arbide, for example ally comprising from ofthe composition sten carbide.

carbide and other binde iron, manganese and Heretofore cemented carbides have been employed extensively as bits for cutting tools. Such bits are relatively thick and mounted on suitable While attempts have been made'to manufacture thin-cutting disks of the, order of 11g inch in' thicknes material, it has been imp ent invention,

line-grained disk which woul of taking a smooth, sharp, unsupported in a lateral direction.

Cemented carbide is ordinarily somewhat brit-` tle but when formed into very thin sections, it is so brittle that it is practically impossible to grind such a disk to a ne, smooth cutting edge. In addition to brittleness,'it is diicult to produce very thin plates of cemented carbide `that will lie perfectly flat. Very thin plates of this material whether produced by squirting or by the process outlined in the above Schrter patents are somewhat porous and coarse-grained and have a tendency to' become warped when ired at the sintering temperature, If thin plates are made by the hot-press methods disclosed in the copending ap- L. Hoyt, Serial No. 181,536,

and in Gilson Patent No.

supporting shanks.

to produce 4a s plication of Samuel tiled April 6, 1927, 1,756,857. such plates are brittle and also coarse- In the prior processes for making cemented carbide, the powdered materials from which the cemented carbide is made' are usually in direct member a, 1930, serial No. d this application February 593,543 v' f contact for an appreciable period of time' either with a carbon boat or mold during the sintering operation, It is my present opinion that this contact with'carbon for an appreciable time at a high temperature is the main cause of the brittleness4 and coarse-grained structure found in very thin plates Aformed by prior processes Graphite has a tendency to absorb cobalt at the sintering temperature of cemented tungsten carbide and this action tends to increase the brittleness of thecemented material. Coarsenessof the grain'structure also has the same effect and this latter condition is a, function of the time vduringyvhich the cementing material is heated vat the sintering temperature. l

In my copending application Serial No. 363,- 079, led May 13, 1927, I have disclosed a method .for producing thin plates ofcemented carbide. which are supported laterall coextensive molybdenum pl sintered platesare supported as discl above application, it 4'is possible vto produce a sharp cutting edge on thedisk. The method disclosed inrmy prior application however is not suitablevfor the production of l ported thin plates of cemen 'type described in the presen Inl my prior application, Serial No. 462,368, filed June 19, 1930, I have disclos whereby a hard, tough and grained, cemented carbide may be produced by simultaneously applying heat and pressure in a Ty OFFICE y by Asubstantially ed an apparatus unusually finevacuum to powdered materials comprising a hard metal composition. I employ the apparatus dis-' closed in the latter application in carrying out the present invention.

vide a hard, tough, uniforml without lateral support.

The novel features which I believe to be characteristic of my invention are set forthwith par-- ticularity in the appended claims. The invention itself however will best be understood from reference to the following specication whenconsidered in connection with the accompanying drawing' in which Fig. 1 represents a view partly in section-and partly in elevation of an apparatuswhereby my'invention may be carried into effect. Fig. 2 is a View partly in section and`partly in elevation on an enlarged scale of a portion oi? the apparatus disclosed in Fi 3 and 4 are detail views of portions of the apparatus disclosed in Figfl. l

g. 1, while Figs.

I extension 12 on plate 11.

Referring tothe drawing, I- have indicated at 1 a-receptacle having a removablev cover or closure member 2 and .a base portion 3. Extending through the latter is a screw-threaded plug 4 provided with an opening-5 extending therethrough, the latter opening connecting with passageways 6 and 'I in an extension 8 mounted on the upper end of the plug4. The closure member 2 is provided with a central upwardly extending guide portion 9 adapted to accommodate a movable rod 10, The rod 10 is provided at its lower end with an extension 10' and carries at its upper end a at metal plate 11 provided with an extension 12.\ Plate 11 is of smaller diameter than closure member 2 and is connected-to the latterl by means of a corrugated flexible member 13, commonly known as a sylphon bellows. The portion of the member 2 which separates the interior of the sylphon from the interior of receptacle 1fis perforated with holes 14 whereby the pressure within the sylphon bellows 13 and the receptacle 1 may be equalized.

Pressure may be applied to the plate 11 through a lever 15 pivoted provided with a depending portion 17 which is pivoted to'lever 15 and adapted to engage the A weight (not shown) may be positionedat any desired point lalong the lever 15 in order to apply a suitable pressure to the plate 11. If desired, however, the standard 16 and lever 15 may be omittedand pressure applied to plate 11 by the atmosphere only, as hereinafter disclosed.

In fabricating small cemented carbide metal cutting disks, for example disks about 0.15 inch in diameter, a hard glass tube 18 is employed as the mold, the latter having an interior diameter substantially equal to the diameter/of the disks to be fabricated, a wall thickness` about Va inch or greater, and a length ofv about 4 ches ori less.

Plungers 19 and 20, made of iron or steel or other suitable metal, are mounted in opposite ends of the `mold 18. The plungers are each about 2 inches long and provided with central holes 21 and 22 respectively. These holes extend in a lengthwise or axial direction about one-halfway through the plungers and accommodate a removable or temporary plug 23, about 30 milsin diameter, which is preferably made oi' quartz but may be made of graphite.

In carrying out my inventionl'the tubular glass mold 18 is loaded by placing it in a vertical position, inserting the lower plunger 20 therein to the extent of about 1/2 inch, then fixing the graphite rod 23 in the hole 22 of the plunger.

disk 24 having4 a central opening therein ofthe same diameter as the graphite rod 23 is slid over the rod23 so as to rest on the upper end of the plunger 20. Pulverized cemented tungsten carbide 2 5, for example a powdered mixture consisting of about 13% cobalt and about 87%'tungsten carbide in sufficient quantity to produce a sintered disk of about 1/64 inch thick and about 0.15 inch diameter, is weighed out and placed on the graphite disk 24. `The powdered material is .levelled by means of a relatively long rod (not shown) which maybe provided with a central opening therethrough. This, rod is nserted in the upper end of the glass mold 18 over the graphite rod 23 and rotated until the powdered material 25 is levelled. The levelling rod is then removed and successive alternate layers of graphite 24 and powdered material 25 inserted and levelled in the mold- 18 until the latter is filled to the desired extent. Plunger 19 to a standard 16 and 4may be supplementedl by ,lever 15. As in my copending application Serial is then inserted in the upper end of the mold and the 'latter positioned in receptacle 1 between extensions 8 and 10 as indicated in Fig. 1. 'Ihe extensions 10 and 8 are provided with adjustable bearing sleeves 26 and 27 respectively which accommodate the outer ends of the plungers 19 and 20 and center mold 18 inreceptacie 1 and hold. the plungers rigidly in such positions that their axes always fall along the same line.

When the mold 18 has been placed in position, the receptacle 1 is flushed out with hydrogen which may be supplied through the opening 5 in the plug 4. After the hydrogen supply is cut off the receptacle is evacuated by means of a pumpy to plug 4. When a desired degree of vacuum has been attained an electric circuit is closed, as in my prior application Serial No. 462,368, through a suitable (not shown) connected ysourceof current-supply (not shown) connected almost instantly to the desired temperature and as they become heated plunger 19 descends and the powdered materials are compressed into a hard, tough, metallic composition whichis uniformly fine grained and capable of taking a Very fine smooth cutting edge.

If a glass tube is employed as the mold, the process may be observed clearly. When the electric circuit is closed the graphite disks within the mold are heated to a .visible redness increasing to incandescence. `In the meantime the sections of mixed tungsten carbide and cobalt powders are heated to their sintering temperature partly by radiation from the carbon disks and partly by the electric current which flows through the powdered material. At the instant when the various fseparate portions of powdered material arrive at `their .sintering temperature, each portion is simultaneously compressed to about one-half its original thickness. I his compression of all the disks is completed in merely' a fraction of a second., The electric heating circuit is then opened and hydrogen gas re-admitted to the receptacle 1. The mold 18 and plungers 19 and 20 are removed from receptacle 1 hot plunged into water thereby breaking themold and permitting removal of the pressed disks.

Ordinarily, atmospheric pressure alone is suiiicient to compress the powdered material to the desired thickness. This pressure however No. 462,368, the heating current may, if desired, be supplied to the pressed material4 for a predetermined length of time after the powdered materials have been pressed to the desired thickness, the circuit being controlled, as in the prior application, by a switch 28 mounted on the outer end of lever 15. y

Since mold 18 is electrically non-conducting, it ispractically a cold mold and therefore a very high pressure may be applied to the sintered material. Moreover, since the powdered materials are heated for an unusually short period -of time, for example for about 1/300th or 1/500th of the time required to hot press similar powdered materials according to the process disclosed lin the above Hoyt application or ('rilsor'i patent, there is practically no opportunity either for grain growth in the pressed material or for absorption of cobalt by the carbon disks. tough and uniformly fine-grained product isv oband while still pressure applied to thev .as a result, a very hard,4

tained which maybe supplied cutting edge.

Cutting disks produced according torny process have a hardness ofabout 90 to 92 on the Rockwell A scale. While these disks may be supplied ,with a keen smooth cutting edge, this cannot ordinarily be done with the usual grinding apparatus but may be accomplished by a grinding wheel made of a mixture of cemented tungsten carbide and diamond powder as disclosed in my copending application Serial No. 357,536 filed April 23, 1929.

The small graphite disks may be 'prepared by cutting off sections of suitable thickness from a graphite rod of the same diameter. The graphite disks keep the sintercd disks separate from one another and also prevent plungers 19 and 20 from sticking vto the pressed material.

Instead of weighing the separate portions 25` of mixed powdered materials so as to .obtain an exact quantity of material in each disk, I may squirt a tube made from a suitable mixture of 4tungsten carbide, cobalt and starch paste, remove I may hot press in a similar mannera mixture of diamond dust andcemented tungsten carbide with a smooth keen such as disclosed in the copending application Serial No. 357,536 and form for example disk saws as thin as Il; inch and 1/2 inch diameter. While such materiall is not as strong as cemented tungsten carbide alone, its strength may be materially increased by the addition of small molybdenum wires thereto. These wires should be about 0.010 inch in diameter and preferably in the shape of .a C or 0 about 312 inch in diameter. The addition of about 2% by weight of these wires to cemented tungsten carbide and diamond dust should give it sufficient ,strength to withstand the strain produced in sawing hard materials such as sapphire while the narrow swath and speed of cutting of4 such a wheel should give it an efficiency far exceeding that of any small abrasive saw now in use. Small molybdenum wires may alsoiif desired be added to the cemented tungsten carbide powdered materials in the proportions indicated above. The molybdenum wires in either case act to reinforce the pressed powdered material in much the same way that steel reinforces concrete.

vWhat I claim as new and desire to secure by Letters Patent of the United States is:

1. A hard, tough, cemented carbide disk having reinforcing wires .embedded therein.

2. A hard, tough, metallic disk consisting largely of cemented tungsten carbide, said disk having reinforcing molybdeunm wires embedded therein.

3. A hard, tough, cutting disk having a thick- 3 rness of 1/64 inch or less, said disk consisting of a diamond impregnated cemented carbide having reinforcing wires embedded therein.

GEORGE Ff'rAYI'R. 3 

